1. Field of the Invention
The present invention relates to a pivot bearing apparatus for axially supporting rotating members including swing arms carrying magnetic heads for recording and reproducing signals on disks.
2. Description of the Related Art
Recently, a miniaturized and lighter-weight disc has been greatly demanded. In doing so, memory density of a disc (such as a hard disc) in the disc device has been increased, with the result that the width of a track for writing signals has become narrower and narrower. A magnetic head for recording signals on and reproducing the same from the disc is mounted on the swing arm of an actuator. The magnetic head is brought to a required recording and reproducing position on the disc by swinging the swing arm. Thus, high rotational positioning accuracy must be achieved. Since the actuator having the swing arm is supported on an actuator block by the pivot bearing assembly, the positioning accuracy of the swing arm is determined by the rotational accuracy of the pivot bearing assembly.
The conventional pivot bearing assembly comprises a shaft, two bearings surrounding the shaft and each having an inner race and an outer race, rolling elements such as balls disposed between them and a sleeve in which those two bearings are inserted. Even if the pivot bearing assembly is miniaturized, its structure and its number of constituent components are unchanged.
When a radially inward directed pressure is applied to the outer races of the bearings, the radial clearance between the balls and the outer race of the pivot bearing assembly becomes smaller, causing friction between the balls and the raceway grooves formed in the outer rings of the bearings. This increases the driving torque for rotating the pivot bearing assembly, and, therefore, the bearings rotate very heavily.
When the bearings are mounted on the shaft and/or the sleeve of the pivot bearing assembly in an inclined state, the radial clearance of the pivot bearing assembly becomes unstable, creating torque fluctuation and/or torque spike. This brought up unstable rotation of the pivot bearing assembly, causing an adverse effect on the positioning accuracy of the swing arm.
Further, if the actuator block and the pivot bearing assembly are displaced from each other due to a temperature change, this can result in writing and reading-out errors on a recording medium such as a disk device.
Still further, there is a problem that, since the pivot bearing assembly is miniaturized, very small external vibration cannot be absorbed and/or resonance is apt to occur.
These problems would be solved by increasing the dimensional accuracy and rigidity of the constituent components. However, the number of the constituent components is not changed. In addition thereto, the dimensional accuracy of the constituent components must be improved extremely and the machining cost is greatly increased. Thus, the manufacturing cost of the pivot bearing assembly cannot be reduced. In some cases, it is very difficult to machine the constituent components at such a high accuracy. Further, in order to miniature the constituent components, they must be made very thin or fine. Thus, the rigidity of not only the constituent components but also the pivot bearing assembly cannot be maintained at a high level. Still further, since two inner rings are adhered to the shaft and two outer rings are adhered to the sleeve, many portions must be adhered together, causing unavoidable production of out-gas.
An object of the present invention is to provide a pivot bearing assembly which is miniaturized and wherein manufacturing process and manufacturing cost can be decreased by reducing the number of components, wherein rigidity of the main components is enhanced to lessen the adverse effect caused by the external stress applied to the sleeve and the outer rings, and wherein assembly accuracy of the components is increased to prevent run-out, irregular rotation, change in torque and/or generation of torque spike.
Another object of the present invention is to reduce generation of out-gas.
In order to achieve the objects of the present invention, a pivot bearing assembly comprises a shaft having one end portion forming a reduced portion and the other end portion forming a cylindrical main body coaxial with the reduced portion, first inner ring means disposed on the outer periphery of the reduced portion, second inner ring means integrally formed in the outer periphery of the main body, outer ring means and coaxially surrounding the first and second inner ring means and extending from one end portion of the shaft to the other end portion of said shaft, rolling elements rollably arranged between the first inner ring means and the outer ring means and between the second inner ring means and the outer ring means, and a tolerance ring mounted on the outer periphery of the outer ring means.
The outer ring means comprises an outer ring portion extending from said one end portion of the shaft to the other end portion of the shaft and coaxially surrounding the shaft and a sleeve portion supporting the tolerance ring and surrounding the outer ring portion.
The outer ring means can comprise a cylindrical outer ring which coaxially surrounds the first and second bearings, and a cylindrical sleeve tightly mounted on the outer periphery of the outer ring.
Alternatively, the outer ring means can comprise a cylindrical outer ring portion and a cylindrical sleeve portion integrally forming the outer portion of the outer ring means.
A tolerance ring for elastically connecting the sleeve means to an actuator block is received in a receiving portion formed in the outer peripheral surface of the sleeve portion.
The tolerance ring can have a substantially trapezoidal longitudinal cross section and a transversal cross section with a shape of a circularly arranged series of saw-teeth or a corrugated form.
The receiving portion can comprise an annular groove extending from one end portion of the sleeve portion to the other end portion of the sleeve portion.
Alternatively, the receiving means can comprise annular receiving grooves respectively formed in one end portion and the other end portion of the sleeve portion for receiving the lateral ends of the tolerance ring.
Alternatively, the receiving mean can comprise annular grooves formed in one end portion and the other end portion of the sleeve portion and snap rings held in the annular grooves.
Alternatively, the first inner ring means can comprise an inner ring, and the second inner ring means can comprise an annular groove formed in the outer periphery of the main body portion of the shaft and a portion of the main body portion in the vicinity of the annular groove in the main body portion. The annular groove in the main body portion is adapted to receive the rolling elements.